The memory device is getting more complex in nowadays due to the capacity thereof is demanded to be larger, such that the packaging process of which becomes more and more difficult correspondingly. Accordingly, more failed memory cells will be occurred due to the integration thereof is higher during the fabricating process. Therefore, more capacity of the memory device, higher integration of memory cells will be, proportionally, more failed memory cells will be occurred, and further, the yield of memory device will be affected certainly.
Generally, a redundant memory array is used to improve the yield. The redundant memory array consists of redundant memory cells, which is provided around the main memory array for being used to replace the failed memory cells while the failed memory cells have occurred. Therefore, the yield can be improved efficiently since the redundant memory array is applied during the fabricating process.
In detail, the individual redundant memory array is respectively connected to the corresponding bit line and the corresponding word line of the main memory array through a fuse. Thus, when a failed memory cell is occurred and going to be repaired, the corresponding fuse will be blown by a laser light beam or a high voltage to be as the open state. Equally, replacing the failed memory cell by the redundant memory cell is according to the blowout fuse. Oppositely, if there is nothing required for being repaired, then the fuse is still remaining to be the close state. Therefore, the fuse is capable of being programmed regarding to the address within the main memory array can be repaired while the failed memory cells have occurred.
Due to the fuse can be blown by the laser light beam, the laser machine has to be used; however, which is inconvenient for moving while the failed memory cells is repairing. Furthermore, the repairing period is too long, and the cost thereof will be increase. Additionally, while the memory device has packaged, the failed memory cells cannot be further repaired since that are found thereafter.